I. Field of the Invention
The present invention relates generally to a value actuator, and more particularly, to a novel drive engagement between the valve actuator and a valve rotatable member.
II. Description of the Prior Art
There are a wide variety of different types of valve actuators used throughout industry, and likewise, a plurality of previously known valve actuators for each different type of valve. With the "rising stem" type of valve, which is commonly used as an oil pipeline valve or the like, a rotatable member threadably engages an elongated valve stem. The rotatable member is fixed against axial movement while, conversely, the stem is fixed against rotational movement so that rotation of the rotatable member axially moves the valve stem to thereby actuate the valve.
In order to actuate the so-called "rising stem" valves, it has been the previous practice to connect a handwheel, crank or the like to the rotatable member in order to effect rotation thereof. A handwheel or crank does not give sufficient mechanical advantage to be useful where large valves of high fluid pressures are involved. Also the valve stem in such assemblies is subjected to wear and tear from the natural elements and even to vandalism. Moreover, it has been found that attachment and removal of the actuating wheel tends to damage the valve stem as the handwheels bang against the valve stem due to carelessness of the workmen. Lastly, since the valve stem moves axially through the center of the handwheel, the valve stem itself tends to interfere with the natural cranking action of the workman.
In order to solve these difficulties, more complex valve actuators have been devised in which a gear arrangement is provided for drivingly engaging the rotatable member. A disadvantage of these previously known actuators, however, is that the actuators themselves are unnecessarily complex and require extensive tooling during their production which, of course, increases the cost of the actuator. In particular, many of the previously known valve actuators utilize an interdigital clutch mechanism between the actuator and the valve rotatable member for drivingly engaging the same. These previously known interdigital clutch assemblies are not only expensive to manufacture, but also are prone to failure.
Moreover, many of these previously known valve actuators require extensive modifications of the valve which is not only expensive but often time impractical, particularly when the valve is already installed in the field.